Aluminum base alloy containing copper and beryllium and method of making the same



Patented Feb. 12, 1946 ALUMINUM BASE ALLOY CONTAINING COP- PER. AND BERYLLIUM AND METHOD OF MAKING THE SAME Richards H. Harrington, Schenectady, N. 1., alsignor to General Electric Company, a corporation of New York No Drawing. Application March as, 1942,. Serial No. 436,607

Claims. (Cl. 148-2L1) The present invention is a precipitation hardened aluminum-copper-beryllium alloy and a method for making it. While such alloys are not unknown, so far as I am aware the prior art alloys of that composition do not possess unusual properties. I have discovered that aluminumcopper-beryllium alloys which are completely precipitation hardened and in which the copper and beryllium are present in a certain specific relation with respect to each other have unexpected high physical properties. Beryllium has a greater affinity for copper than for aluminum. In an alloy consisting of aluminum, beryllium and copper with the copper and beryllium present in about the ratio of 7:1, full precipitation treatment of the alloy leaves a minimum of copper and beryllium remaining in solid solution. This condition results in maximum tensile properties and unusually high elastic properties and hardness.

In carrying out the present invention I employ an aluminum-ccpper-beryllium alloy in which the copper and beryllium are in the ratio of about 7:1 as in the compound CuBe, for example an alloy containing 3.5% copper, 0.5% beryllium with the remainder aluminum. The alloy ingredients may be melted and alloyed in any suitable furnace for example a gas or oil fired crucible furnace or a high frequency furnace. For economical and metallurgical purposes I prefer to add a master alloy containing 12.5% beryllium and 87.5% copper to molten aluminum to thereby obtain the desired alloy composition. Beryllium in excess of the 7:1 ratio adds nothing to the usefulness of the alloy, increases the cost, decreases the elongation, and may actually cause some injury. Also, beryllium in excess of 0.75%, even when balanced with copper, will cause a decrease in the useful properties of the alloy.

In the fabrication of the alloy the aluminum is melted and the temperature of the melt raised to about 800 to 850 C. The required amount of the copper-beryllium master alloy is then added plus an excess of about 0.02% to 0.05% beryllium to act as a deoxidizer. No flux is employed. The alloy melt is allowed to just freeze in the crucible and is then remelted, heated to about 700 to 715 C. and poured. The freezing and remelting substantially eliminates any gas (chiefly H) which is dissolved during the first melting and heating of the alloy to the higher temperature. Thereafter the alloy is heated for a few hours, for example about four hours to an elevated temperature, for example about 540 C. to produce a condition 01 solid solution in the alloy.

It is quenched from this temperature preferably in water, then aged by reheating for several hours, for example eight, at a temperature of about 150 to 200 C. If desired the alloy may be cold reduced about 10 to or more after the quench and for best results such cold reduction should immediately follow the quench. Very desirable properties are obtained with a cold reduction of about 36% but further improvement may be obtained by extending the cold reduction up to about 50%.

The improvement in properties attained by a precipitation hardened aluminum-oopper-beryllium alloy containing copper and beryllium in the ratio of 7:1 is indicated by comparison with a similar alloy in which the copper and beryllium are in the ratio of 19:1. As an example of the two alloys we may consider the following compositions:

(1) Per cent Copper Beryllium Aluminum in which the ratio of the copper to beryllium is 7:1.

(2) Per cent 3.8 0.2

Copper Beryllium Aluminum tion hardening treatments for example a solution treatment at temperatures varying from 510 to 570 C. a quench from those temperatures, and a reheat for periods of time varying from 2 to 20 hours at temperatures ranging from 50 to 300 C. It was found that solution temperatures of 530 to 550 C. and aging temperatures of 100 to 225 C. develop useful properties in the alloy but that the preferred complete heat treatment to yield maximum properties in each case comprises maintaining the alloy at a temperature of about 540 C. for four hours. quenching, preferably in water, and reheating for eight hours at 200 C. The Rockwell B hardness of alloys (1) and (2) after the preferred heat treatment was to 57 and 45 to 48 respectively which result clearly indicates a high degree of superiority for the alloys containing copper and beryllium in the ratio of 7:1.

The following additional properties of alloys (1) and (2) indicate a considerable superiority for the alloy containing the preferred critical :ratio of copper and beryllium:

The present alloy aged at 200 C. has considerable superiority with respect to stability at elevated temperatures when compared with well known commercial aluminum alloys which are precipitation hardened at lower temperatures,

for example 155 to 160 C. For example alloy No. 1 must be aged at 250 C. before its hardness falls into the hardness range of prior art aluminum base alloys which have been aged at 155 to 160 C.

Aluminum base alloys containing copper and beryllium in the ratio of 7: 1, as well as aluminum base alloys containing copper and beryllium in other ratios, age naturally, for example the solution-quenched alloy may be permitted to age at room temperature. If the aluminum base alloy containing copper and beryllium in the ratio of 7 :1 is quenched from the 540 solution treatment and then aged naturally the Rockwell B hardness will increase from 27 as quenched to 51 at the end of four weeks which may be compared with the Rockwell B hardness 55 obtained by complete precipitation heat treatment. The aluminum base alloy containing 3.8% copper and 0.2%

beryllium, after quenching from 540 C. has a- Rockwell B hardness varying from -1 as quenched to 38 at the end of four weeks which may be compared with the Rockwell B hardness 45 obtained by a complete precipitation heat treatment.

After overaging (annealing) in the temperature range of 300 to 450 C. aluminum-copperberyllium alloys may be cold reduced about to depending upon the shape of the cross section of the alloy. This breaks up the cast structure. Reannealing permits further cold working and, upon subsequent complete precipitation heat treatment, such cold working effects some improvement in properties over the cast heat treated alloy particularly with respect to elongation.

The maximum efiect of cold work is accomplished by introducing it between the solution quench and precipitation reheat. The cold working should be carried out soon after the quench, for example within one hour after quenching for alloy No. 1 indicated above, and Within one day for alloy No. 2. Cast rods one inch in diameter and consisting of alloys No. 1 and No. 2, when quenched from 540 C. may be cold reduced 36% quite easily when the reduction is carried out promptly after the quench. The eifect of cold reduction on physical properties of the alloy is indicated by the following tests. Alloy No. 1 containing 3.5% copper, 0. beryllium, balance aluminum was heated four hours at 540 C., water quenched, cold reduced 36% and then aged eight hours at 150 C. Alloy No. 2 containing 3.8% copper, 0.2% beryllium, balance aluminum was given the same heat The above properties may be further improved if the alloy is cold reduced up to 50%.

Although I prefer to employ aluminum base alloys containing copper and beryllium in the ratio of 7:1, my improved heat treatment may be applied with useful results to aluminum base alloys containing other ratios of copper and beryllium provided the beryllium content of the alloy does not materially exceed 0.75% by weight.

The present heat treatment may also be applied with advantage to aluminum base alloys containing copper and beryllium, as indicated above, to which a small quantity of cobalt is added, for example particularly good results are obtained if the cobalt and beryllium are present in the ratio of 6.5:1 and the copper in the range of 2 to 6%. In such an alloy the ratio of copper to beryllium is not critical but the atomic ratio of about 65:1 for the cobalt and beryllium is critical with copper present in quantities preferably varying from about 2.5 to 4.5%.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An alloy containing 1.75 to 5.2% copper, 0.25% to 0.7% beryllium with the balance substantially all aluminum, said copper and beryllium being present in the alloy in the critical ratio of 7 :1.

2. A precipitation hardened alloy containing 1.75 to 5.2% copper, 0.25 to 0.75% beryllium with the balance substantially all aluminum, the copper and beryllium being present in said alloy in the critical ratio of 7:1.

3. A precipitation hardened alloy containing about 3.5% copper and about 0.5% beryllium with the remainder substantially all aluminum, said alloy having a Rockwell B hardness of at least 55, a tensile strength of at least 44,000 pounds per square inch, a proportional liimt of at least 25,000 pounds per square inch, and an elongation in 2 inches of about 5%.

4. The method of precipitation hardening an aluminum base alloy containing 1.75 to 5.2% copper, and 0.25 to 0.75% beryllium, with the balance substantally all aluminum, said copper and beryllium being present in the critical ratio of 7:1, which comprises heating the alloy to a temperature of about 520 to 550 C. to effect a condition of solution, quenching the alloy and reheating it to temperatures of about C. to 225 C.

5. The method of precipitation hardening-an aluminum base alloy containing 1.75 to 5.2%

copper and 0.25 to 0.75% beryllium, with the balance substantially aluminum, said copper and beryllium being present in the critical ratio of 7 :1, which comprises heating the alloy to a temperature of about 520 to 550 C. to effect a condition of solution, quenching the alloy, cold reducing it about 20% to 60%, and reheating the product to' temperatures of about 100 C. to 225 C.

RICHARDS H. HARRINGTON.

Certificate of Correction Patent No. 2,394,546. 7 February 12, 1946.

' RICHARDS H. HARRINGTON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 34, claim 1, for 0.25% to 0.7% read 0.25 to 0.75%; line 48, claim 3, for liimt read limit; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 24th day of September, A. D. 1946.

LESLIE FRAZER,

First Assistant Oommissioner of Patents. 

